Thin-Film Transistor Sensor and Method of Manufacturing the TFT Sensor

ABSTRACT

According to an aspect of the present invention, there is provided a thin-film transistor (TFT) sensor, including a bottom gate electrode on a substrate, an insulation layer on the bottom gate electrode, an active layer in a donut shape on the insulation layer, the active layer including a channel through which a current generated by a charged body flows, an etch stop layer on the active layer, the etch stop layer including a first contact hole and a second contact hole, and a source electrode and a drain electrode burying the first and second contact holes, the source and drain electrodes being disposed on the etch stop layer so as to face each other.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application based on pending application Ser. No.13/185,630, filed Jul. 19, 2011, the entire contents of which is herebyincorporated by reference.

BACKGROUND

1. Field

The present invention relates to thin-film transistors (TFTs), and moreparticularly, to a TFT sensor having an oxide semiconductor layer as anactive layer.

2. Description of the Related Art

Performance of a thin-film transistor (TFT) greatly depends on thematerial and state of an active layer in which a channel, through whichcharge carriers move, is formed.

In the case of TFTs having an active layer formed of amorphous silicon(hereinafter, referred to as an amorphous silicon TFT), charge mobilityis very low, namely, about 0.5 cm²/Vs.

In the case of TFTs having an active layer formed of polycrystallinesilicon (hereinafter, referred to as polycrystalline silicon TFTs), acrystallization process, an impurity-implantation process, an activationprocess, etc. are required, and thus a manufacturing process thereof iscomplicated and a manufacturing cost thereof is high, compared toamorphous silicon TFTs.

SUMMARY

The present invention provides a thin-film transistor (TFT) sensorcapable of stably detecting a touch intensity and a touch direction of acharged body.

According to an aspect of the present invention, there is provided athin-film transistor (TFT) sensor, including a bottom gate electrode ona substrate, an insulation layer on the bottom gate electrode, an activelayer in a donut shape on the insulation layer, the active layerincluding a channel through which a current generated by a charged bodyflows, an etch stop layer on the active layer, the etch stop layerincluding a first contact hole and a second contact hole, and a sourceelectrode and a drain electrode burying the first and second contactholes, the source and drain electrodes being disposed on the etch stoplayer so as to face each other.

The active layer may have a generally square or rectangular donut shape,and the first and second contact holes may be disposed on corner areasof the active layer so as to diagonally face each other.

The first and second contact holes may be formed on edges of the activelayer so as to face each other.

The TFT sensor may further including a first top gate electrode and asecond top gate electrode on the etch stop layer, the first and secondtop gate electrodes being on a same level as the source and drainelectrodes without contacting the source and drain electrodes, the firstand second top gate electrodes facing each other.

A direction of current flowing in the channel may be controlled byapplying a periodically-swinging voltage to the first and second topgate electrodes.

The active layer may include a hole at the center of the active layer,and the channel may be divided into channels by the hole.

A touch direction and a touch intensity of the charged body may besensed based on the amounts of currents flowing through the channelsinto which the channel is divided.

The active layer may include an oxide semiconductor.

The bottom gate electrode may include a first bottom gate electrode anda second bottom gate electrode that correspond to edges of the activelayer, the first and second bottom gate electrodes being a predetermineddistance apart from each other and disposed so as to face each other.

The direction of current flowing in the channel may be controlled byapplying a periodically-swinging voltage to the first and second bottomgate electrodes.

According to another aspect of the present invention, there is provideda thin-film transistor (TFT) sensor, including a bottom gate electrodeon a substrate, an insulation layer on the bottom gate electrode, anactive layer in a donut shape on the insulation layer, the active layerincluding a hole for channel separation at the center of the activelayer, an etch stop layer on the active layer, the etch stop layerincluding a first contact hole and a second contact hole, and anelectrode layer on the etch stop layer corresponding to areas of edgesof the active layer.

The active layer may have a generally square or rectangular donut shapehaving four corners, the first and second contact holes may besymmetrically disposed on two corners, diagonally facing each other,from among the four corners of the active layer, and the electrode layermay include a source electrode and a drain electrode that bury the firstand second contact holes and are symmetrically disposed on the twocorners, and a first top gate electrode and a second top gate electrodethat are symmetrically disposed at the two remaining corners withoutcontacting the source and drain electrodes.

The direction of current flowing in the channel may be controlled byapplying a periodically-swinging voltage to the first and second topgate electrodes.

The active layer may have four edges, the first and second contact holesmay be symmetrically disposed on two edges, facing each other, fromamong the four edges of the active layer, and the electrode layer mayinclude a source electrode and a drain electrode that bury the first andsecond contact holes and are symmetrically disposed on the two edges,and a first top gate electrode and a second top gate electrode that aresymmetrically disposed on the two remaining edges without contacting thesource and drain electrodes.

The active layer may include an oxide semiconductor.

The active layer may include at least one material selected from thegroup of In, Ga, Zn, Sn, Sb, Ge, Hf, Al, and As.

The active layer may be square or rectangular.

According to another aspect of the present invention, there is provideda thin-film transistor (TFT) sensor, including a first bottom gateelectrode and a second bottom gate electrode separated from each otherby a predetermined distance on a substrate, an insulation layer on thefirst and second bottom gate electrodes, an active layer in a donutshape on the insulation layer, the active layer including a hole forchannel separation at the center of the active layer, an etch stop layeron the active layer, the etch stop layer including a first contact holeand a second contact hole, and a source electrode and a drain electrodeburying the first and second contact holes, the source and drainelectrodes being disposed on the etch stop layer so as to face eachother.

The active layer may have four edges, the first and second contact holesmay be symmetrically disposed on two edges, facing each other, fromamong the four edges of the active layer, and the source and drainelectrodes may bury the first and second contact holes and aresymmetrically disposed on the two edges, and the first and second bottomgate electrodes are symmetrically formed on the two remaining edges.

The active layer may include an oxide semiconductor.

The active layer may include at least one material selected from thegroup of In, Ga, Zn, Sn, Sb, Ge, Hf, and As.

The direction of current flowing in the channel may be controlled byapplying a periodically-swinging voltage to the first and second bottomgate electrodes.

The active layer may be square or rectangular.

According to another aspect of the present invention, there is provideda thin-film transistor (TFT) sensor array including TFT sensors arrangedby rotating a TFT sensor by a predetermined angle, wherein each of theTFT sensors includes a bottom gate electrode on a substrate, aninsulation layer on the bottom gate electrode, an active layer in adonut shape on the insulation layer, the active layer including a holefor channel separation at the center of the active layer, an etch stoplayer on the active layer, the etch stop layer including a first contacthole and a second contact hole, a source electrode and a drain electrodeburying the first and second contact holes, the source and drainelectrodes being disposed on the etch stop layer so as to face eachother, and a first top gate electrode and a second top gate electrode,the first and second top gate electrodes being disposed on the etch stoplayer so as to face each other.

The TFT sensor array may include four TFT sensors arranged by rotating aTFT sensor at intervals of 90 degrees.

According to another aspect of the present invention, there is provideda thin-film transistor (TFT) sensor array including TFT sensors arrangedby rotating a TFT sensor by a predetermined angle, wherein each of theTFT sensors includes a first bottom gate electrode and a second bottomgate electrode separated from each other by a predetermined distance ona substrate, an insulation layer on the first and second bottom gateelectrodes, an active layer in a donut shape on the insulation layer,the active layer including a hole for channel separation at the centerof the active layer, an etch stop layer on the active layer, the etchstop layer including a first contact hole and a second contact hole, anda source electrode and a drain electrode burying the first and secondcontact holes, the source and drain electrodes being disposed on theetch stop layer so as to face each other.

The TFT sensor array may include four TFT sensors arranged by rotating aTFT sensor by 90 degrees at a time.

The TFT sensor array may include four TFT sensors arranged by rotatingeach of two TFT sensors by 90 degrees.

According to another aspect of the present invention, there is provideda method of manufacturing a thin-film transistor (TFT) sensor, themethod including forming a bottom gate electrode on a substrate, formingan insulation layer on the bottom gate electrode, forming an activelayer that has a donut shape and a hole for channel separation at thecenter of the active layer, the active layer being formed on theinsulation layer, forming an etch stop layer having a first contact holeand a second contact hole, the etch stop layer being formed on theactive layer, and forming a source electrode and a drain electrode thatbury the first and second contact holes and face each other, the sourceand drain electrodes being formed on the etch stop layer.

The active layer may be formed to have a generally square or rectangulardonut shape, and the first and second contact holes may be formed oncorner areas of the active layer so as to diagonally face each other.

The first and second contact holes may be formed on edges of the activelayer so as to face each other.

The method may further include forming a first top gate electrode and asecond top gate electrode on the etch stop layer on the same level asthe source and drain electrodes without contacting the source and drainelectrodes, so as to face each other, simultaneously with the forming ofthe source and drain electrodes.

Forming the bottom gate electrode may include forming a first bottomgate electrode and a second bottom gate electrode that are apredetermined distance apart from each other and face each other, thefirst and second bottom gate electrodes corresponding to areas of theactive layer.

The active layer may include an oxide semiconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent tothose of skill in the art by describing in detail example embodimentswith reference to the attached drawings, in which:

FIG. 1 illustrates a plan view of a thin-film transistor (TFT) sensoraccording to an embodiment of the present invention;

FIGS. 2A and 2B illustrate graphs for explaining a method of driving theTFT sensor illustrated in FIG. 1;

FIGS. 3A through 6B illustrate perspective views and cross-sectionalviews for explaining a method of manufacturing the TFT sensorillustrated in FIG. 1;

FIG. 7 illustrates a plan view of a TFT sensor according to anotherembodiment of the present invention;

FIGS. 8A through 11B illustrates perspective views and cross-sectionalviews for explaining a method of manufacturing the TFT sensorillustrated in FIG. 7;

FIGS. 12A through 12C illustrate a TFT sensor according to anotherembodiment of the present invention;

FIGS. 13A through 13C illustrate a TFT sensor according to anotherembodiment of the present invention;

FIG. 14 illustrates a TFT sensor array according to an embodiment of thepresent invention;

FIG. 15 illustrates a TFT sensor array according to another embodimentof the present invention;

FIGS. 16 and 17 illustrate a plan view and a cross-sectional view of aTFT sensor according to another embodiment of the present invention;

FIGS. 18A and 18B illustrate graphs for explaining a method of drivingthe TFT sensor illustrated in FIG. 16; and

FIG. 19 illustrates a TFT sensor array formed with the TFT sensorillustrated in FIG. 16.

DETAILED DESCRIPTION

Korean Patent Application No. 10-2010-0072479, filed on Jul. 27, 2010,in the Korean Intellectual Property Office, and entitled: “Thin-FilmTransistor Sensor and Method of Manufacturing the TFT Sensor,” isincorporated by reference herein in its entirety.

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

In the description of the present invention, if it is determined that adetailed description of commonly-used technologies or structures relatedto the invention may unnecessarily obscure the subject matter of theinvention, the detailed description will be omitted.

FIG. 1 is a plan view of a thin-film transistor (TFT) sensor accordingto an embodiment of the present invention.

Referring to FIG. 1, the TFT sensor includes an integrated-type bottomgate electrode and a separated-type top gate electrode. The TFT sensorincludes a bottom gate electrode BG. The TFT sensor also includes, onthe bottom gate electrode BG, a first top gate electrode TG1, a secondtop gate electrode TG2, a drain electrode 120D, and a source electrode120S on the same plane.

The bottom gate electrode BG is square and formed on a substrate 100.The bottom gate electrode BG controls a current flowing in a channelformed in an active layer 115. The active layer 115 has a square donutshape, has a separation hole H1 for channel separation, and is formed onthe bottom gate electrode BG. The separation hole H1 is located at thecenter of the active layer 115, and the active layer 115 is formed ofoxide semiconductor.

The size of the separation hole H1 may depend on a static resolvingpower and a direction sensing performance of the TFT sensor. When theseparation hole H1 is bigger, the static resolving power decreases,whereas the direction sensing performance improves. Otherwise, thestatic resolving power increases, whereas the direction sensingperformance degrades.

A drain region and a source region of the active layer 115 contact thedrain electrode 120D and the source electrode 120S via first and secondcontact holes H21 and H22, respectively. The drain electrode 120D andthe source electrode 120S are formed on two corner areas diagonallyfacing each other from among the four corner areas of the square activelayer 115. The first top gate electrode TG1 and the second top gateelectrode TG2 are formed on the two remaining corner areas diagonallyfacing each other on the same level as the drain electrode 120D and thesource electrode 120S.

Because of the separation hole H1, a current Ids flowing from the drainelectrode 120D to the source electrode 1205 may flow through a firstchannel {circle around (1)} passing through the first top gate electrodeTG1 and a second channel {circle around (2)} passing through the secondtop gate electrode TG2. FIGS. 2A and 2B are graphs for explaining amethod of driving the TFT sensor illustrated in FIG. 1.

Referring to FIG. 2A, when a voltage is applied to the bottom gateelectrode BG of the TFT sensor, voltages having different polarities areperiodically applied to the first top gate electrode TG1 and the secondtop gate electrode TG2. At this time, the amount of a sum of currentflowing through the first channel {circle around (1)} and currentflowing through the second channel {circle around (2)}, namely, a totalcurrent Ids, is constant regardless of the time.

When a negative voltage is applied to a top gate electrode TG, a channelnarrows, and thus a current flowing through the channel decreases. Whena positive voltage is applied to the top gate electrode TG, the channelwidens, and thus the current flowing through the channel increases.Accordingly, the current flowing in the channel may be controlled usingthe polarity of a voltage applied to the top gate electrode TG. Thus,the directions of currents flowing through two channels may becontrolled.

For example, when a positive voltage is applied to the first top gateelectrode TG1 and a negative voltage is applied to the second top gateelectrode TG2, most current flows through the first channel {circlearound (1)}. On the other hand, when a negative voltage is applied tothe first top gate electrode TG1 and a positive voltage is applied tothe second top gate electrode TG2, most current flows through the secondchannel {circle around (2)}. In other words, the amount of total currentIds is constant, and the direction of current may be controlled bychanging the amounts of currents flowing through the two channels.

Referring to FIG. 2B, the first top gate electrode TG1 and the secondtop gate electrode TG2 allow currents to flow through the first channel{circle around (1)} and the second channel {circle around (2)},respectively, at different points in time. When there is surface chargedue to contact or non-contact of an external charged body, the amount ofcurrent flowing through the channel of the active layer 115 varies.

For example, when contact or non-contact of the external charged bodyoccurs near the first top gate electrode TG1, current flowing throughthe first channel {circle around (1)} increases (Ids') at the momentwhen the first top gate electrode TG1 is open. When contact ornon-contact of the external charged body occurs near the second top gateelectrode TG2, current flowing through the second channel {circle around(2)} increases (Ids') at the moment when the second top gate electrodeTG2 is open. Accordingly, it is known from the amount of currentincreasing at time intervals that the external charged body has movedfrom the vicinity of the first top gate electrode TG1 to the vicinity ofthe second top gate electrode TG2. In other words, the moving direction(or touch direction) of the external charged body may be determined froma difference between the amounts of currents flowing through the firstand second channels, and a charge intensity (or a touch intensity) ofthe external charged body may be determined from the amounts of thecurrents.

FIGS. 3A through 6B are perspective views and cross-sectional views forexplaining a method of manufacturing the TFT sensor illustrated in FIG.1.

Referring to FIGS. 3A and 3B, the bottom gate electrode BG is formed onthe substrate 100.

The substrate 100 may be formed of a transparent glass material mainlyincluding SiO₂. The substrate 100 may also be formed of a plasticmaterial. The substrate 100 may include a metal foil, a flexiblesubstrate, etc.

Before the bottom gate electrode BG is formed, a buffer layer (notshown) may be formed on the substrate 100. The buffer layer may blockimpurities of the substrate 100 from penetrating into layers stacked onthe substrate 100. The buffer layer may include, e.g., SiO₂ and/orSiN_(x).

The bottom gate electrode BG is formed by forming a metal layer on thesubstrate 100 and patterning the metal layer to have a square shape.Although the metal layer of the bottom gate electrode BG may be formedof a metal or a metal alloy such as Au, Ag, Cu, Ni, Pt, Pd, Al, Mo, W,Ti, an Al:Nd alloy, or a Mo:W alloy, the present invention is notlimited thereto, and other various materials may be used inconsideration of adhesion of the bottom gate electrode BG with aneighboring layer, the flatness of the stacked layers, electricresistance, processability, and the like.

A gate insulation layer 113 is formed on the substrate 100 on which thebottom gate electrode BG has been formed. The gate insulation layer 113may be formed of an insulative material such as silicon oxide (SiO_(x))or silicon nitride (SiN_(x)). For example, the gate insulation layer 113may be a tetraethyl orthosilicate (TEOS) oxide layer. The gateinsulation layer 113 may also be formed of an insulative organicmaterial or the like.

Referring to FIGS. 4A and 4B, the active layer 115 is formed on thesubstrate 100 on which the gate insulation layer 113 has been formed.

The active layer 115 may include an oxide semiconductor including atleast one element selected from the group consisting of In, Ga, Zn, Sn,Sb, Ge, Hf, Al, and As. For example, the oxide semiconductor may includeat least one selected from the group consisting of ZnO, SnO₂, In₂O₃,Zn₂SnO₄, Ga₂O₃, and HfO₂. The active layer 115 may be formed oftransparent oxide semiconductor. Examples of the transparent oxidesemiconductor may include Zinc Oxide, Tin Oxide, Ga-In-Zn Oxide, In-ZnOxide, In-Sn Oxide, and the like, and the present invention is notlimited thereto.

The active layer 115 may be formed by sputtering, which is a physicaldeposition method. The active layer 115 may be formed by controlling theflux of oxygen according to a resistance required by the TFT sensor. Theactive layer 115 is formed by forming an oxide semiconductor layer onthe gate insulation layer 113 and patterning the oxide semiconductorlayer to have a square shape corresponding to the bottom gate electrodeBG.

The separation hole H1 is formed at the center of the active layer 115so as to expose a portion of the gate insulation layer 113. The activelayer 115 has a square donut shape because of the separation hole H1.The separation hole H1 may penetrate from the gate insulation layer 113to the bottom gate electrode BG.

Referring to FIGS. 5A and 5B, an etch stop layer 117 is formed on thesubstrate 100 on which the active layer 115 has been formed.

The etch stop layer 117 may be formed of an insulative material such asSiO_(x) or SiN_(x), but the present invention is not limited thereto.The etch stop layer 117 may be formed by low-temperature chemical vapordeposition (CVD).

The etch stop layer 117 buries the separation hole H1 of the activelayer 115. The etch stop layer 117 includes the first and second contactholes H21 and H22 formed in two of the four corner areas of the squareactive layer 115 so as to be symmetrical to each other. The first andsecond contact holes H21 and H22 expose the drain and source regions ofthe active layer 115, respectively.

Referring to FIGS. 6A and 6B, the drain electrode 120D, the sourceelectrode 120S, and the first and second top gate electrodes TG1 and TG2are formed on the substrate 100 on which the etch stop layer 117 hasbeen formed.

The drain electrode 120D, the source electrode 120S, and the first andsecond top gate electrodes TG1 and TG2 may be formed by forming a metallayer on the etch stop layer 117 and patterning the metal layer intofour electrodes. The metal layer is formed of a conductive material. Theconductive material may be a metal such as Cr, Pt, Ru, Au, Ag, Mo, Al,W, Cu, or AlNd, or a conductive oxide such as ITO, GIZO, GZO, AZO, IZO(i.e., InZnO), or AZO (i.e., AlZnO). The metal layer may be the same asthe metal layer used to form the bottom gate electrode BG.

The drain electrode 120D is formed on one corner area of the squareactive layer 115 by burying the first contact hole H21, and the sourceelectrode 120S is formed on the corner area diagonally facing the drainelectrode 120D by burying the second contact hole H22. Alternatively,the source electrode 1205 may be formed on the first contact hole H21,and the drain electrode 120D may be formed on the second contact holeH22. The drain electrode 120D and the source electrode 120S may contactthe drain region and the source region of the active layer 115 via thefirst and second contact holes H21 and H22, respectively.

The first and second top gate electrodes TG1 and TG2 are formed on thetwo remaining corner areas, respectively, in which the first and secondcontact holes H21 and H22 are not formed, so as to be symmetrical toeach other.

A passivation layer (not shown) may be formed on the first and secondtop gate electrodes TG1 and TG2, the drain electrode 120D, and thesource electrode 120S. The passivation layer may be formed of aninsulative material such as SiO_(x) or SiN_(x). An insulative materialor the like may be further included to form the passivation layer.

FIG. 7 is a plan view of a TFT sensor according to another embodiment ofthe present invention.

Referring to FIG. 7, the TFT sensor includes an integrated-type bottomgate electrode and a separated-type top gate electrode. The TFT sensorincludes a bottom gate electrode BG. The TFT sensor includes, on thebottom gate electrode BG, a TFT including a first top gate electrodeTG1, a second top gate electrode TG2, a drain electrode 220D, and asource electrode 220S on the same plane.

The bottom gate electrode BG is square and formed on a substrate 200. Anactive layer 215 has a square donut shape, has a separation hole H1 forchannel separation, and is formed on the bottom gate electrode BG. Theseparation hole H1 is located at the center of the active layer 215, andthe active layer 215 is formed of oxide semiconductor.

The size of the separation hole H1 may depend on a static resolvingpower and a direction sensing performance of the TFT sensor. When theseparation hole H1 is bigger, the static resolving power decreases,whereas the direction sensing performance improves. Otherwise, thestatic resolving power increases, whereas the direction sensingperformance degrades.

A drain region and a source region of the active layer 215 contact thedrain electrode 220D and the source electrode 220S via first and secondcontact holes H21 and H22, respectively. The drain electrode 220D andthe source electrode 220S are formed at the center of two facing edges(long edges or short edges) of the four edges of the square active layer215. The first top gate electrode TG1 and the second top gate electrodeTG2 are formed on the remaining edges facing each other on the samelevel as the drain electrode 220D and the source electrode 220S.

Because of the separation hole H1, a current Ids flowing from the drainelectrode 220D to the source electrode 220S may flow through a firstchannel {circle around (1)} passing through the first top gate electrodeTG1 and a second channel {circle around (2)} passing through the secondtop gate electrode TG2.

A method of driving the TFT sensor of FIG. 7 is the same as thatdescribed above with reference to FIGS. 2A and 2B, and thus a detaileddescription thereof will be omitted.

FIGS. 8A through 11B are perspective views and cross-sectional views forexplaining a method of manufacturing the TFT sensor illustrated in FIG.7.

Referring to FIGS. 8A and 8B, the bottom gate electrode BG is formed onthe substrate 200.

The substrate 200 may be formed of a transparent glass material mainlyincluding SiO₂. The substrate 200 may also be formed of a plasticmaterial. The substrate 200 may include a metal foil and a flexiblesubstrate.

Before the bottom gate electrode BG is formed, a buffer layer (notshown) may be formed on the substrate 200. The buffer layer may blockimpurities of the substrate 200 from penetrating into layers stacked onthe substrate 200. The buffer layer may include SiO₂ and/or SiN_(x).

The bottom gate electrode BG is formed by forming a metal layer on thesubstrate 200 and patterning the metal layer to have a square shape.Although the metal layer of the bottom gate electrode BG may be formedof a metal or a metal alloy such as Au, Ag, Cu, Ni, Pt, Pd, Al, Mo, W,Ti, an Al:Nd alloy, or a Mo:W alloy, the present invention is notlimited thereto, and other various materials may be used inconsideration of adhesion of the bottom gate electrode BG with aneighboring layer, the flatness of the stacked layers, electricresistance, processability, and the like.

A gate insulation layer 213 is formed on the substrate 200 on which thebottom gate electrode BG has been formed. The gate insulation layer 213may be formed of an insulative material such as SiO_(x) or SiN_(x). Forexample, the gate insulation layer 113 may be a TEOS oxide layer. Thegate insulation layer 213 may also be formed of an insulative organicmaterial or the like.

Referring to FIGS. 9A and 9B, the active layer 215 is formed on thesubstrate 200 on which the gate insulation layer 213 has been formed.

The active layer 215 may include oxide semiconductor including at leastone element selected from the group consisting of In, Ga, Zn, Sn, Sb,Ge, Hf, Al, and As. For example, the oxide semiconductor may include atleast one selected from the group consisting of ZnO, SnO₂, In₂O₃,Zn₂SnO₄, Ga₂O₃, and HfO₂. The active layer 215 may be formed oftransparent oxide semiconductor. Examples of the transparent oxidesemiconductor may include Zinc Oxide, Tin Oxide, Ga-In-Zn Oxide, In-ZnOxide, In-Sn Oxide, or the like, but the present invention is notlimited thereto.

The active layer 215 may be formed by sputtering, which is a physicaldeposition method. The active layer 215 may be formed by controlling theflux of oxygen according to a resistance required by the TFT sensor. Theactive layer 215 may be formed by forming an oxide semiconductor layeron the gate insulation layer 213 and patterning the oxide semiconductorlayer to have a square shape corresponding to the bottom gate electrodeBG.

The separation hole H1 is formed at the center of the active layer 215so as to expose a portion the gate insulation layer 213 formed below theactive layer 215. The active layer 215 has a square donut shape becauseof the separation hole The separation hole H1 may penetrate from thegate insulation layer 213 to the bottom gate electrode BG.

Referring to FIGS. 10A and 10B, an etch stop layer 217 is formed on thesubstrate 200 on which the active layer 215 has been formed.

The etch stop layer 217 may be formed of an insulative material such asSiO_(x) or SiN_(x), but the present invention is not limited thereto.The etch stop layer 217 may be formed by low-temperature CVD.

The etch stop layer 217 buries the separation hole H1 of the activelayer 215. The etch stop layer 217 includes the first and second contactholes H21 and H22 formed at the centers of two of the four edges of thesquare active layer 215 so as to be symmetrical to each other. The firstand second contact holes H21 and H22 expose portions of the drain andsource regions of the active layer 215.

Referring to FIGS. 11A and 11B, the drain electrode 220D, the sourceelectrode 220S, and the first and second top gate electrodes TG1 and TG2are formed on the substrate 200 on which the etch stop layer 217 hasbeen formed.

The drain electrode 220D, the source electrode 220S, and the first andsecond top gate electrodes TG1 and TG2 may be formed by forming a metallayer on the etch stop layer 217 and patterning the metal layer intofour electrodes. The metal layer is formed of a conductive material. Theconductive material may be a metal such as Cr, Pt, Ru, Au, Ag, Mo, Al,W, Cu, or AlNd, or a conductive oxide such as ITO, GIZO, GZO, AZO, IZO(i.e., InZnO), or AZO (i.e., AlZnO). The metal layer may be the same asthe metal layer used to form the bottom gate electrode BG.

The drain electrode 220D buries the first contact hole H21 and is formedat the center of one edge of the square active layer 215. The sourceelectrode 220S buries the second contact hole H22, is formed at thecenter of one edge of the square active layer 215, and symmetricallyfaces the drain electrode 220D. Alternatively, the source electrode 220Smay be formed on the first contact hole H21, and the drain electrode220D may be formed on the second contact hole H22. The drain electrode220D and the source electrode 220S may contact the drain region and thesource region of the active layer 215 via the first and second contactholes H21 and H22, respectively.

The first and second top gate electrodes TG1 and TG2 are formed on theremaining edges, respectively, in which the first and second contactholes H21 and H22 are not formed, so as to symmetrically face eachother.

A passivation layer (not shown) may be formed on the first and secondtop gate electrodes TG1 and TG2, the drain electrode 220D, and thesource electrode 220S. The passivation layer may be formed of aninsulative material such as SiOx or SiNx, and an insulative material orthe like may be further included to form the passivation layer.

FIGS. 12A through 12C illustrate a TFT sensor according to anotherembodiment of the present invention.

Referring to FIGS. 12A through 12C, the TFT sensor includes a TFTincluding first and second top gate electrodes TG1 and TG2, a drainelectrode 320D, and a source electrode 320S on the same plane on abottom gate electrode BG. The TFT sensor according to the presentembodiment is rectangular and accordingly is different from the TFTsensor of FIG. 1, which is square. A detailed description of the samecontents as those of the TFT sensor of FIG. 1 will be omitted.

The bottom gate electrode BG is rectangular and formed on a substrate300. Before the bottom gate electrode BG is formed, a buffer layer (notshown) may be formed on the substrate 300. A gate insulation layer 313is formed on the bottom gate electrode BG. An active layer 315 has aseparation hole H1 for channel separation, and is formed on the gateinsulation layer 313. The active layer 315 is formed of oxidesemiconductor, and has a rectangular donut shape because of theseparation hole H1 extending along a long edge of the active layer 315at the center of the active layer 315. A drain region and a sourceregion of the active layer 315 are exposed through first and secondcontact holes H21 and H22 formed in an etch stop layer 317 on the activelayer 315. The first and second contact holes H21 and H22 extend alongshort edges of the rectangular active layer 315 so as to symmetricallyface each other. The drain electrode 320D and the source electrode 320Sare formed on the etch stop layer 317 and bury the first contact holeH21 and the second contact hole H22, respectively. The drain electrode320D and the source electrode 320S contact the drain region and thesource region, respectively, of the active layer 315. The drainelectrode 320D and the source electrode 320S are formed along the shortedges of the rectangular active layer 315 so as to symmetrically faceeach other. The first and second top gate electrodes TG1 and TG2 areformed along the long edges of the rectangular active layer 315 on thesame level as the drain electrode 320D and the source electrode 320S soas to symmetrically face each other. The first and second top gateelectrodes TG1 and TG2 neither overlap with nor contact the drainelectrode 320D and the source electrode 320S.

Because of the separation hole H1, a current Ids flowing from the drainelectrode 320D to the source electrode 320S may flow through a firstchannel {circle around (1)} passing through the first top gate electrodeTG1 and a second channel {circle around (2)} passing through the secondtop gate electrode TG2. A method of driving the TFT sensor of FIG. 12Ais the same as that described above with reference to FIGS. 2A and 2B,and thus a detailed description thereof will be omitted.

FIGS. 13A through 13C illustrate a TFT sensor according to anotherembodiment of the present invention.

Referring to FIGS. 13A through 13C, the TFT sensor includes a TFTincluding first and second top gate electrodes TG1 and TG2, a drainelectrode 420D, and a source electrode 420S on the same plane on abottom gate electrode BG. The TFT sensor according to the presentembodiment is rectangular and accordingly is different from the TFTsensor of FIG. 1, which is square. A detailed description of the samecontents as those of the TFT sensor of FIG. 1 will be omitted.

Before the bottom gate electrode BG is formed, a buffer layer (notshown) may be formed on a substrate 400. A gate insulation layer 413 isformed on the bottom gate electrode BG. An active layer 415 has aseparation hole H1 for channel separation, and is formed on the gateinsulation layer 413. The active layer 415 is formed of oxidesemiconductor, and has a rectangular donut shape because of theseparation hole H1 extending along long edges of the rectangular activelayer 415 at the center of the active layer 415. A drain region and asource region of the active layer 415 are exposed through first andsecond contact holes H21 and H22 formed in an etch stop layer 417 on theactive layer 415. The first and second contact holes H21 and H22 areformed along the long edges of the rectangular active layer 415 so as tosymmetrically face each other. The drain electrode 420D and the sourceelectrode 420S are formed on the etch stop layer 417 and bury the firstcontact hole H21 and the second contact hole H22, respectively. Thedrain electrode 420D and the source electrode 420S contact the drainregion and the source region, respectively, of the active layer 415. Thedrain electrode 420D and the source electrode 420S are formed along thelong edges of the rectangular active layer 415 so as to symmetricallyface each other. The first and second top gate electrodes TG1 and TG2are formed along short edges of the rectangular active layer 415 on thesame level as the drain electrode 420D and the source electrode 420S soas to symmetrically face each other. The first and second top gateelectrodes TG1 and TG2 neither overlap with nor contact the drainelectrode 420D and the source electrode 420S.

Because of the separation hole H1, a current Ids flowing from the drainelectrode 420D to the source electrode 420S may flow through a firstchannel {circle around (1)} passing through the first top gate electrodeTG1 and a second channel {circle around (2)} passing through the secondtop gate electrode TG2. A method of driving the TFT sensor of FIG. 13Ais the same as that described above with reference to FIGS. 2A and 2B,and thus a detailed description thereof will be omitted.

FIG. 14 illustrates a TFT sensor array according to an embodiment of thepresent invention.

Referring to FIG. 14, the TFT sensor array is formed by arranging aplurality of TFT sensors by changing the direction of a TFT clockwise orcounterclockwise at intervals of 90 degrees. For example, the embodimentof FIG. 14 is a sensor in which an array (including a first TFT A, asecond TFT B obtained by rotating the first TFT A by 90 degreesclockwise, a third TFT C obtained by rotating the second TFT B by 90degrees clockwise, and a fourth TFT D obtained by rotating the third TFTC by 90 degrees clockwise) constitutes a single sensing cell. Each TFTincludes a first top gate electrode TG1, a second top gate electrodeTG2, a drain electrode D, and a source electrode S on the same plane.This array structure may be used to form a sensor having a highdirection sensitivity with respect to left, right, up, and downdirections.

FIG. 15 illustrates a TFT sensor array according to another embodimentof the present invention.

Referring to FIG. 15, the TFT sensor array is formed by arranging aplurality of TFTs by changing the direction of a TFT by 90 degrees. Theembodiment of FIG. 15 is a sensor in which an array (including a firstTFT A, a second TFT B obtained by rotating the first TFT A by 90 degreescounterclockwise, a third TFT C having the same structure as the secondTFT B, and a fourth TFT D obtained by rotating the third TFT C by 90degrees clockwise) constitutes a single sensing cell. TFTs existing on adiagonal line have the same structure. Each TFT includes a first topgate electrode TG1, a second top gate electrode TG2, a drain electrodeD, and a source electrode S on the same plane. Such an array structurecan overlap the intensities of currents in the same direction with eachother, and thus a sensor sensitive to the current can be formed.

Although a TFT sensor array using the TFT sensor of FIG. 1 isillustrated in the embodiments of FIGS. 14 and 15, the TFT sensors ofFIGS. 7, 12A, and 13A may be used to form the TFT sensor array.

FIGS. 16 and 17 illustrate a TFT sensor according to another embodimentof the present invention.

Referring to FIGS. 16 and 17, the TFT sensor includes a separated-typebottom gate electrode. Referring to FIGS. 16 and 17, the TFT sensorincludes a first bottom gate electrode BG1 and a second bottom gateelectrode BG2. The TFT sensor also includes a drain electrode 520D and asource electrode 520S formed on the first and second bottom gateelectrodes BG1 and BG2 so as to be perpendicular to the first and secondbottom gate electrodes BG1 and BG2.

The first and second bottom gate electrodes BG1 and BG2 are formed apredetermined distance apart from each other on a substrate 500. Thesubstrate 500 may be formed of a transparent glass material mainlyincluding SiO₂. The substrate 500 may also be formed of a plasticmaterial. The substrate 500 may include a metal foil, a flexiblesubstrate, etc.

Before the first and second bottom gate electrodes BG1 and BG2 areformed, a buffer layer (not shown) may be formed on the substrate 500.The buffer layer may block impurities of the substrate 500 frompenetrating into layers stacked on the substrate 500. The buffer layermay include SiO₂ and/or SiN_(x).

Although the first and second bottom gate electrodes BG1 and BG2 may beformed of a metal or a metal alloy such as Au, Ag, Cu, Ni, Pt, Pd, Al,Mo, W, Ti, an Al:Nd alloy, or a Mo:W alloy, the present invention is notlimited thereto, and other various materials may be used inconsideration of adhesions of the first and second bottom gateelectrodes BG1 and BG2 with a neighbor layer, the flatness of thestacked layers, electric resistance, processability, and the like.

A gate insulation layer 513 is formed on the first and second bottomgate electrodes BG1 and BG2. The gate insulation layer 513 may be formedof an insulative material such as SiO_(x) or SiN_(x). For example, thegate insulation layer 513 may be a TEOS oxide layer. The gate insulationlayer 513 may also be formed of an insulative organic material or thelike.

An active layer 515 has a separation hole H1 for channel separation, andis formed on the gate insulation layer 513. The active layer 515 isformed of oxide semiconductor, and has a square or rectangular donutshape because of the separation hole H1 formed at the center of theactive layer 515.

The active layer 515 may include oxide semiconductor including at leastone element selected from the group consisting of group III elements andgroup IV elements such as In, Ga, Zn, Sn, Sb, Ge, Hf, Al, and As. Forexample, the oxide semiconductor may include at least one selected fromthe group consisting of ZnO, SnO₂, In₂O₃, Zn₂SnO₄, Ga₂O₃, and HfO₂. Theactive layer 515 may be formed of transparent oxide semiconductor.Examples of the transparent oxide semiconductor may include Zinc Oxide,Tin Oxide, Ga-In-Zn Oxide, In-Zn Oxide, In-Sn Oxide, and the like, andthe present invention is not limited thereto.

An etch stop layer 517 is formed on the active layer 515. The etch stoplayer 517 includes a first contact hole H21 and a second contact holeH22 formed along two edges of the square or rectangular active layer 515so as to be symmetrical to each other. The first and second contactholes H21 and H22 are formed perpendicularly to the first and secondbottom gate electrodes BG1 and BG2.

The etch stop layer 517 may be formed of an insulative material such asSiO_(x) or SiN_(x), but the present invention is not limited thereto.The etch stop layer 517 may be formed by low-temperature CVD.

The drain electrode 520D and the source electrode 520S are formed on theetch stop layer 517. The drain electrode 520D and the source electrode520S may contact the drain and source regions of the active layer 515via the first and second contact holes H21 and H22, respectively.Portions of the drain electrode 520D and the source electrode 520S areoverlapped by respective facing ends of the first and second bottom gateelectrodes BG1 and BG2 and by the other respective facing ends thereof,respectively.

The first and second bottom gate electrodes BG1 and BG2 of the TFTtransistor including the separated-type bottom gate electrode, that is,a bottom gate separation type TFT, serve as the first and second topgate electrodes TG1 and TG2 of the TFT including an integrated bottomgate electrode and a separated top gate electrode.

Although a square TFT sensor is illustrated in FIGS. 16 and 17, a TFTsensor using a rectangular active layer may also have the same structureas that of the square TFT sensor.

FIGS. 18A and 18B are graphs for explaining a method of driving the TFTsensor illustrated in FIG. 16.

Referring to FIG. 18A, voltages having different polarities areperiodically applied to the first and second bottom gate electrodes BG1and BG2 of the TFT sensor. At this time, the amount of a sum of thecurrent flowing to the first channel {circle around (1)} and a currentflowing to the second channel {circle around (2)}, namely, a totalcurrent Ids, is constant regardless of time. The current flowing in achannel may be controlled using the polarities of the voltages appliedto the first and second bottom gate electrodes BG1 and BG2. Thus, thedirections of currents flowing to two channels may be controlled.

For example, when a positive voltage is applied to the first bottom gateelectrode BG1 and a negative voltage is applied to the second bottomgate electrode BG2, most current flows through the first channel {circlearound (1)}. When a negative voltage is applied to the first bottom gateelectrode BG1 and a positive voltage is applied to the second bottomgate electrode BG2, most current flows through the second channel{circle around (2)}. In other words, the amount of the total current Idsis constant, and the direction of the current may be controlled bychanging the amounts of currents flowing through the two channels.

Referring to FIG. 18B, when there is surface charge due to contact ornon-contact of an external charged body with an upper surface of a TFT,the amount of current flowing through the channel of the active layer515 varies. For example, when contact or non-contact of the externalcharged body occurs near the first bottom gate electrode BG1, thecurrent flowing through the first channel {circle around (1)} increasesinstantly (Ids'). When contact or non-contact of the external chargedbody occurs near the second bottom gate electrode BG2, the currentflowing through the second channel {circle around (2)} increasesinstantly (Ids'). Accordingly, it is known that the charged body hasmoved from the vicinity of the first bottom gate electrode BG1 to thevicinity of the second bottom gate electrode BG2. In other words, themoving direction (or touch direction) of the external charged body maybe determined from a difference between the amounts of currents flowingthrough the first and second channels, and a charge intensity (or touchintensity) of the external charged body may be determined from theamounts of the currents.

FIG. 19 illustrates a TFT sensor array formed with the TFT sensorillustrated in FIG. 16.

Referring to FIG. 19, the TFT array is formed by arranging a pluralityof TFT sensors by changing the direction of a TFT only by 90 degrees.The embodiment of FIG. 19 is a sensor in which an array (including afirst TFT A, a second TFT B obtained by rotating the first TFT A by 90degrees counterclockwise, a third TFT C having the same structure as thesecond TFT B, and a fourth TFT D obtained by rotating the third TFT C by90 degrees clockwise) constitutes each sensing cell. TFTs existing on adiagonal line have the same structure.

Although the above-described embodiments describe NMOS transistors forconvenience of explanation, the present invention may also be applied toPMOS transistors including a p-type active layer. The p-type activelayer may be a Cu oxide layer (CuBO₂ layer, CuAlO₂ layer, CuGaO₂ layer,CuInO₂ layer, or the like), a Ni oxide layer, a Ti-doped Ni oxide layer,a ZnO-based oxide layer doped with at least one of a group I element, agroup II element, and a group V element, a ZnO-based oxide layer dopedwith Ag, a PbS layer, a LaCuOS layer, or a LaCuOSe layer.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

1-17. (canceled)
 18. A thin-film transistor (TFT) sensor, comprising: afirst bottom gate electrode and a second bottom gate electrode separatedfrom each other by a predetermined distance on a substrate; aninsulation layer on the first and second bottom gate electrodes; anactive layer in a donut shape on the insulation layer, the active layerincluding a hole for channel separation at the center of the activelayer; an etch stop layer on the active layer, the etch stop layerincluding a first contact hole and a second contact hole; and a sourceelectrode and a drain electrode burying the first and second contactholes, the source and drain electrodes being disposed on the etch stoplayer so as to face each other.
 19. The TFT sensor as claimed in claim18, wherein: the active layer has four edges, the first and secondcontact holes are symmetrically disposed on two edges, facing eachother, from among the four edges of the active layer, and the source anddrain electrodes bury the first and second contact holes and aresymmetrically disposed on the two edges, and the first and second bottomgate electrodes are symmetrically formed on the two remaining edges. 20.The TFT sensor as claimed in claim 18, wherein the active layer includesan oxide semiconductor.
 21. The TFT sensor as claimed in claim 20,wherein the active layer includes at least one material selected fromthe group of In, Ga, Zn, Sn, Sb, Ge, HHf, and As.
 22. The TFT sensor asclaimed in claim 18, wherein the direction of current flowing in thechannel is controlled by applying a periodically-swinging voltage to thefirst and second bottom gate electrodes.
 23. The TFT sensor as claimedin claim 18, wherein the active layer is square or rectangular. 24-25.(canceled)
 26. A thin-film transistor (TFT) sensor array comprising TFTsensors arranged by rotating a TFT sensor by a predetermined angle,wherein each of the TFT sensors includes: a first bottom gate electrodeand a second bottom gate electrode separated from each other by apredetermined distance on a substrate; an insulation layer on the firstand second bottom gate electrodes; an active layer in a donut shape onthe insulation layer, the active layer including a hole for channelseparation at the center of the active layer; an etch stop layer on theactive layer, the etch stop layer including a first contact hole and asecond contact hole; and a source electrode and a drain electrodeburying the first and second contact holes, the source and drainelectrodes being disposed on the etch stop layer so as to face eachother.
 27. The TFT sensor array as claimed in claim 26, comprising fourTFT sensors arranged by rotating a TFT sensor by 90 degrees at a time.28. The TFT sensor array as claimed in claim 26, comprising four TFTsensors arranged by rotating each of two TFT sensors by 90 degrees.29-34. (canceled)